The invention relates to a laser nozzle usable in laser beam cutting, having a movable element comprising a skirt that allows the cutting gas to be funneled into the cutting kerf, and furthermore being easier to implement industrially.
Laser beam cutting requires the use of a nozzle, generally made of copper, that channels the gas and allows the laser beam to pass. The gas and the beam propagate as far as the part to be cut through an axial passage that passes through the body of the nozzle. These nozzles typically have outlet orifice diameters comprised between 0.5 and 3 mm for a working distance comprised between 0.6 and 2 mm.
In order to enable cutting, it is necessary to use high pressures, in general several bars, in the focusing head in order to ensure the gas penetrates into the kerf and flushes out the molten metal.
However, a large percentage of the gas used, typically between 50 and 90%, does not take part in the cutting process, i.e. in the expulsion of molten metal, because it is lost to the sides of the cutting kerf.
These gas losses are in fact due to the enormous difference between the flow cross-sectional area of the nozzle orifice and the size of the focal spot. Thus, by way of indication, the flow cross-sectional area of a nozzle with an outlet orifice of diameter equal to 1.5 mm is 25 times larger than the cross-sectional area of the focal spot created by the laser beam passing through this nozzle.
However, if an insufficient amount of gas penetrates into the kerf, cutting defects will be observed to appear, in particular attached burrs and/or oxidation marks.
Attempting to solve this problem by decreasing the diameter of the orifice of the nozzle is not ideal because the risk is then taken that the laser beam will strike and deteriorate the interior of the nozzle. Decreasing the diameter of the orifice of the nozzle moreover also decreases cutting quality and/or performance.
There are moreover a number of documents proposing various solutions that attempt to encourage gas to penetrate into the kerf, documents EP-A-1669159, JP-A-62006790, JP-A-61037393, JP-A-63108992, JP-A-63040695, U.S. Pat. No. 4,031,351, U.S. Pat. No. 3,383,491, DE 198 53 765 C1 and JP-A-2003-260582 for example.
However, none of these solutions is truly ideal because they either have an architecture that is complicated to implement, are excessively bulky relative to conventional nozzles and/or have limited effectiveness.
Document U.S. Pat. No. 3,383,491 in particular discloses a laser cutting nozzle comprising a movable element the end of which is pressed by a spring against the surface of the part to be cut in order to encourage the injection of the cutting gas into the kerf. Document DE 198 53 765 C1 also describes a spring having a similar effect.
This solution poses a certain number of problems. On the one hand, the force exerted by the spring in the direction of the sheet causes the movable element to exert a substantial force on the sheet to be cut. There is therefore a risk that the sheet will be deformed, scratched or even dragged by the movable element, as in general the sheet is simply placed on the table of the cutting machine. On the other hand, the device is complicated to implement and substantially bulkier than conventional laser nozzles. This poses a problem in the context of the cutting of imbricated parts, i.e. parts that are located very close together on a given sheet. However, this type of cutting is widely employed in the industry of laser cutting because of the material savings procured thereby.
An alternative solution has been proposed in French patent application No. 1,154,224 filed 16 May 2011 and unpublished at the date of filing of the present application. It consists in arranging a movable element in the body of a laser nozzle. This movable element is able to move axially in said body, in the direction of the surface of the sheet to be cut, under the effect of a gaseous pressure. The movable element thus moves toward the upper surface of the sheet to be cut until it makes contact therewith. The movable element thus forms a skirt that channels and concentrates the cutting gas into the kerf, thereby forcing the gas to penetrate into said kerf and improving its effectiveness.
However, this solution is not ideal because the movable element must be arranged within the very body of the laser nozzle, more precisely in the axial passage of the body of the nozzle.
Thus, there is a need to provide a solution that increases the effectiveness of the gas and that furthermore can be easily implemented via a simple modification of existing and widely commercially available laser nozzles, without modifying their internal geometry.
These conventional laser nozzles have various geometries, each model being dedicated to one type of cutting process, one type of laser beam, one type of focusing head, etc. With regard to industrial implementation, it is therefore essential to provide a solution that is compatible with most, or even all, of these nozzles.
However, the bodies of many nozzles used in the laser cutting industry do not contain a sufficient volume of material for it to be possible to arrange therein an axial housing for an internal movable element according to French patent application No. 1 154 224.
Furthermore, certain cutting applications require what are referred to as “dual flow” nozzles to be used, these nozzles comprising, in addition to an axial gas passage, at least one lateral gas passage passing through the nozzle body and arranged in proximity to said axial passage. The presence of this or these additional passages makes it difficult to machine a housing in the body of the nozzle, i.e. to widen the initial axial passage in order to allow an internal movable element to be placed therein.
Moreover, the solution consisting in arranging a movable element in the axial passage of a conventional nozzle, without widening said passage beforehand, is unsatisfactory since it decreases the space available for the passage of the focused laser beam. This results in a risk of heating or even deterioration of the internal walls of the movable element and/or the nozzle body, which would also decrease cutting performance and/or quality and the productivity of the process.
The problem addressed is thus that of how to mitigate all or some of the aforementioned drawbacks by providing a laser nozzle that especially allows the effectiveness of the gas used in laser cutting to be improved, while being much easier to implement industrially and of much improved lifespan relative to existing solutions, and that is furthermore compatible with most, even all, existing conventional laser nozzles.